Medical procedures often require locating and treating target areas within a patient. Radiation therapy and many surgical procedures require locating the target with a high degree of precision to limit collateral damage to healthy tissue around the target. It is particularly important to know or estimate the precise location of the target in radiation oncology because it is desirable to limit the exposure of adjacent body parts to the radiation. In applications for treating prostate cancer, for example, the colon, bladder or other body parts of the patient adjacent to the prostate are desirably not impinged by the high-intensity radiation beam. Surgical applications, such as breast surgery and other procedures involving soft tissue, also require knowing the precise location of a target because a lesion is not necessarily fixed relative to external landmarks on the patient.
Many imaging systems have been used to locate areas or particular targets within a body before performing radiation oncology or surgical procedures. Although x-ray, Magnetic Resonance Imaging (MRI), CT, and other imaging techniques are useful to locate targets within the body at the pre-operative stage of a procedure, they are often not suitable or difficult to use in real time during surgery or radiation therapy. For example, the location of a lesion in soft tissue or an organ within the patient's body may shift relative to external landmarks on the patient between the pre-operative imaging procedure and the actual radiation or surgical procedure. Additionally, when imaging systems are used during a radiation or surgical procedure, they may not provide sufficiently accurate measurements of the location of the lesions and they may interfere with the radiation or surgical procedure. Therefore, imaging techniques by themselves are not suitable for accurately identifying the actual location of a target for many medical applications.
Another technique to locate a target in a patient is to implant a marker relative to the target. For example, implantable markers that generate a signal have been proposed for use to locate a selected target in a patient in radiation oncology procedures. U.S. Pat. No. 6,385,482 B1 issued to Boksberger et al. (Boksberger) discloses a device having an implanted emitter unit located inside or as close as possible to a target object and a plurality of receiver units that are located outside of the patient. Boksberger discloses determining the location of the target object by energizing the emitter unit using a generator and sensing the signal from the emitter unit with the receiver units. Boksberger discloses and claims that the receiver units are configured to determine the gradient of the magnetic field generated by the emitter unit. Boksberger discloses emitter units that are energized using a wired connection to the external generator. Boksberger also indicates that it is conceivable to use an emitter unit that is energized by a battery or excited by an electromagnetic field generated by the external generator. The wired emitter units disclosed in Boksberger, however, may not be suitable for use in radiation oncology and many surgical procedures because it is impractical to leave a wired emitter unit implanted in a patient for the period of time of such procedures (e.g., five to forty days).
Another technique to locate a target in a patient is to implant passive, gold fiducials in or near the target site. The positions of the gold fiducials are determined periodically using radiation. Although gold fiducials are useful for localizing a target within a patient, these systems do not provide sufficiently accurate real time measurements of the target site location during radiation oncology procedures.
One practical difficulty of using wired markers or gold fiducials is implanting the objects in the patient. Boksberger, for example, discloses positioning the emitter unit at a desired site in the body by percutaneously inserting a hollow puncture needle into the patient and then passing a tube through the hollow puncture needle. After the tube is in place, Boksberger further discloses passing the emitter unit through the tube to position the emitter unit at or near the target within the patient. This is a cumbersome process because a tube is left in the patient during the radiation procedure to provide a passageway to remove the leads and the emitter unit. Moreover, the emitter units must be loaded into the tubes by skilled personnel at the healthcare provider. Thus, implanting wire markers is cumbersome, inefficient, and not well suited for radiation oncology applications that require a patient to return for treatments over a period of five to forty days.
Another process for percutaneously implanting objects in a patient is brachytherapy for treating prostate cancer. In brachytherapy, radioactive sources or “seeds” are implanted relative to a tumor to provide a high dose of radiation to the tumor, but not the healthy tissue surrounding the tumor. FIGS. 1A and 1B are cross-sectional views of a two-piece introducer 100 of the prior art used in brachytherapy. Referring first to FIG. 1A, the introducer 100 includes a needle 102 and a stylet 104 slidably disposed within the needle 102. The stylet 104 includes a first handle 101 and a blunt distal end 106. The needle 102 includes a second handle 103 and a cannula 108 extending through the second handle 103. The cannula 108 is configured to hold radioactive seeds 110 or other objects. The cannula 108 has a distal tip 105 configured to percutaneously penetrate the patient for implantation of the seeds 110 in the patient. Inert spacers 111 can be used to provide the desired spacing between the seeds 110 when they are implanted in the patient. The seeds 110 and spacers 111 are retained in the cannula 108 by a plug 112 made from bone wax or other suitable bio-compatible materials.
To implant the desired arrangement of seeds 110 at a target location in a patient, an operator pushes the cannula 108 in a first direction (arrow A) to insert the tip 105 into the patient. The operator then pushes the second handle 103 further in the first direction to position the tip 105 at the desired depth within the patient where the seeds 110 are to be implanted. Throughout this motion, the operator moves the needle 102 and the stylet 104 together as a unit. At the desired depth, the operator grasps the first handle 101 with one hand and the second handle 103 with the other hand. At this point, the operator attempts to hold the first handle 101 stationary while simultaneously sliding the second handle 103 back in a second direction (arrow B) toward the first handle 101. As shown in FIG. 1B, this movement causes the cannula 108 to slide over the seeds 110 and the spacers 111 to implant them in the patient. In many situations, however, the operator moves the first handle 101 in the first direction (arrow A) while sliding the second handle 103 back in the second direction (arrow B). This causes the stylet 104 to push the seeds 110 out of the cannula 108, which can cause the seeds 110 to move laterally away from the axis of the cannula (i.e., a “train wreck”). Thus, one concern of the prior art introducer 100 is misplacement of the seeds 110.
Another concern of the prior art introducer 100 used in brachytherapy applications is that a skilled operator typically loads a specific pattern of seeds and spacers into an introducer at the facility of a healthcare provider according to the specific needs of each particular patient. In most brachytherapy applications it is necessary to arrange the seeds and spacers at the hospital or clinic according to the specific parameters of each patient because the location and shape of the tumors vary among different patients. Arranging and loading the seeds for each patient is a time consuming process that requires skilled personnel and is subject to human error. Therefore, the techniques for inserting or implanting objects in the patients used in brachytherapy are not desirable in other applications.